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    <meta charset="UTF-8">
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    <title>Document</title>
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<body>
    <script>

        let arr = [1,2,3,4,5,4,3,2,1]


        // 数组去重
        let res = [...new Set(arr)]
        console.log(res)

        // 交集
        let arr2 = [4,5,6,5,4]
        let s2 = new Set(arr2)
        // let res2 = [...new Set(arr)].filter((item)=>{
        //     return s2.has(item)
        // })
        let res2 = [...new Set(arr)].filter(item => new Set(arr2).has(item))
        console.log(res2) // 4 5 


        // 并集
        let union = [...new Set([...arr,...arr2]) ]
        console.log(union)


        // 差集

        let diff = [...new Set(arr)].filter(item => !new Set(arr2).has(item))
        console.log(diff)

    </script>
</body>
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